Enzymes often catalyze substrate oxidation or reduction by concerted electron and proton transfer events. Electrons are typically channelled through a transition metal center while coupled to proton transfers at other residues in the active site pocket. This often occurs in a concerted fashion with substantial spacial separation of the e– and H+. This presentation will describe a number of different types of such multiple-site PCET processes. Synthetic iron-porphyrin systems with connected bases are being used as models for heme active sites. As the distance between the heme and the base increases, the intrinsic MS PCET rate constants decrease. The molecule shown below, with a phenol-base coupled to a photoexcitable anthracene, is a unimolecular model for tyrosine oxidations. This molecule undergoes very rapid excited state MS-CPET at high to very low temperatures, with a very small temperature dependence. One extreme in separation is the removal of a hydrogen atom by transferring to two different molecules, for instance forming an oxyl radical XO● from XOH + oxidant + base. Such termolecular reactions are quite facile under some conditions. These various results will be interpreted using theoretical models.

Concerted multiple-site proton-coupled electron transfer (MS-PCET): Separating the proton and electron

251st National Meeting (2016)

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